Medicaid Family Care Act of 1990 - Amends title XIX (Medicaid) of the Social Security Act to provide federally reimbursed Medicaid coverage of alcoholism and drug dependency residential treatment services for pregnant women whose family income is below 185 percent of the Federal poverty level and for their Medicaid-eligible children and spouses. Lists the required services included in such coverage as: (1) individual, group, and family counseling and addiction education and treatment provided pursuant to individualized treatment plans; (2) room and board in a structured environment with on-site supervision 24 hours a day; (3) therapeutic child care; (4) parental assistance in obtaining developmental assistance for their preschool children and public education for themselves and their school-age children; (5) easier access to other health, social, and child care services; (6) planning and assistance in reentering society; and (7) continuing specialized training of residential treatment facility staff members in the most recent and effective treatment techniques. Requires that such coverage continue for at least 12 months, except that the coverage of pregnant women must continue for one year following the end of pregnancy. Limits the size of a residential treatment facility to no more than 40 beds unless the State provides assurances that a larger facility can furnish the mandatory services.